1. Field of the Invention
The present general inventive concept relates to an image forming apparatus, and more particularly, to a developing unit to develop an electrostatic latent image on a photosensitive medium with developer, and an image forming apparatus having the same.
2. Description of the Related Art
FIGS. 1 and 2 illustrate an example of an image forming apparatus.
In particular, FIGS. 1 and 2 illustrate a color image forming apparatus, which includes a paper feeding unit 10, a plurality of developing units 20, a transfer unit 30, a fusing unit 40, and a paper discharge unit 50.
In such a color image forming apparatus, a sheet of paper is picked up from the paper feeding unit 10, and conveyed past through the developing unit 20 and the transfer unit 30. Accordingly, an image is printed on a surface of the paper sheet, and fixed at the fusing unit 40. After that, the printed paper is discharged out of the image forming apparatus via the paper discharge unit 50.
FIG. 2 illustrates the developing unit 20 in an enlargement view, in which each of the color developing units 20 includes a developing roller 21, a photosensitive medium 22, and a cleaning unit 27 integrally. The developing unit 20 houses developer therein. In such a conventional developing unit 20, it is necessary to agitate the developer sufficiently, before feeding the developer to the developing roller 21, because the developer may inherently develop problems like developer agglomeration and subsequent generation of vertical stripes in printing.
In the implementation of a small image forming apparatus, the developing roller 21, the photosensitive medium 22, and the cleaning unit 27, whether they are in an integrated or separate structure, may have a similar length of lifespan. In certain types of image forming apparatus, however, for example, in an image forming apparatus for office use, generally a large volume of documents are printed out, using up the developer earlier than other components such as a photosensitive medium 22 or a cleaning unit 27 reach their expiration date. This is particularly problematic if all of the components are formed integrally, because other components that can still be used is disposed altogether, to be replaced with a new one having developer therein. Therefore it is important to prepare a removable type of developer cartridge which allows replenishment of developer alone, to save a user's expenditure.
Although the removable type of developer cartridge helps save the user's expenditure for consumables, this type of cartridge can have problems.
That is, a developer feeding unit has to be provided separately, to feed the developer from the developer cartridge to the developing unit. A new agitating structure also has to be provided, to agitate the developer in a manner compatible to the structure of the developer feeding unit, because as mentioned above, printing quality may deteriorate unless the developer is agitated sufficiently.